In recent years, there have been an ever increasing number of vehicles mounting a camera for allowing a driver of the vehicle to view e.g. a scene laterally or rearwardly of the vehicle on a monitor device provided inside the vehicle. Further, there has been developed an apparatus for assisting driving such as driving for parking by effecting e.g. image processing utilizing this camera's captured image. Especially, in the case of a camera configured to capture an image for use e.g. as a basis for generating information to be utilized for positioning of the vehicle, high precision is required in its calibration such as optical axis adjustment. The above-described target position identifying apparatus is used for such calibration processing for the car-mounted camera. For instance, according to one known technique relating to the above technique, a car-mounted camera is used for capturing images of makers (targets) having a black-and-white, checkerboard pattern and disposed at two positions within the field of view of the camera. The center point (calibration point) of the marker is detected through image processing to be utilized for calibration of the car-mounted camera (e.g. Patent Document 1). This technique requires precision detection of the center point of the black-and-white checkerboard pattern. However, depending on the condition of the illuminating light or sunlight, precision of detection of the edge of the white and black regions may become unstable, thus resulting in deterioration in the precision of the maker center point detection.
Also, in the field of art relating to an image scanner provided for effecting precision detection of a target recorded in advance on an original document for the purpose of position alignment of the document, there is known an image signal processing apparatus for effecting the target position detection. In this apparatus, the target is provided in the form of a concentric pattern of red, blue and green regions. Image signals obtained from this target are converted into color difference signals and these color difference signals are used for the target position detection (see Patent Document 2). In this technique, since the color difference signals are utilized for the target detection, availability of sufficient color information (color difference components) of the predetermined target pattern in the captured image signals of the target is the prerequisite for ensuring precision in the position detection. In this regard, in the case of an image scanner, influence from external light is negligible inherently. Hence, it may be considered that precise color difference components are retained in the captured image signals of the target. On the other hand, in the case of target imaging by a car-mounted camera, the imaging (image-capturing) of the target is done under the influence of ambient light. Therefore, with using color difference signals alone, precision target position detection is difficult. Moreover, an erroneous recognition may occur when e.g. some object which looks similar to the pattern of the target is placed inadvertently within the view field of the camera. To avoid this, troublesome management of the working environment will be needed.